Add bulgarian translation

[Pechenikov1]

This PR adds full Bulgarian language support.

Created locale/bg.json with all interface strings translated.

Registered the Bulgarian language in the language selector.

The translation has been tested locally and is working correctly.

[github-actions]

Branch Targeting Suggestion

You've targeted the master branch with this PR. Please consider if a version branch might be more appropriate:

• maintenance-9.x - If your change is backward-compatible and won't create compatibility issues between INAV firmware and Configurator 9.x versions. This will allow your PR to be included in the next 9.x release.

• maintenance-10.x - If your change introduces compatibility requirements between firmware and configurator that would break 9.x compatibility. This is for PRs which will be included in INAV 10.x

If master is the correct target for this change, no action is needed.

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This is an automated suggestion to help route contributions to the appropriate branch.

[sensei-hacker]

Thanks for submitting this!

It appears you ran yarn install locally in a newer environment, which updated package versions. Please remove yarn.lock from the commit. Also, you can't .gitignore a tracked file. One would need to either a) just don;t commit changes to the file or perhaps b) .git/info/exclude

Action required: Please rebase/reset so that yarn.lock and .gitignore are not modified in this PR